First, what is your putter of choice. There are different kinds of putters. For instance, there are straight as hell putters and there are overstable putters. The straight ones work great for everyday play but you will also need a wind putter (overstable) and learn how to throw it. Also, there are different types of putter plastics that can be so soft they droop just from gravity (but tend to get sucked in by the chains on even bad putts) and there are varying degrees of firmer plastics.
Find your zones... There is the "gimmee zone" that is the radius within which you make pretty much every putt attempt. There is the "no sweat zone" which is the radius within which you make more than half of your putts.... and the "hail mary zone" which is the radius within which you pray for divine intervention to make the putt.
You should get atleast two of the same putter (I'd say start with just the straight ones for now) and practice in your no sweat zone after a gimmee zone warm-up. If its going badly go back into the gimmee zone to build up confidence. Work your way back out and see if you can slowly increase the gimmee zone radius. Stay in the gimmee and no sweat zones for practice...there is no need to get frustrated and lose confidence so you want to just build consistency and expand those two zones out slowly but surely.
Otherwise, be an approach shooter during rounds. Just look to get near the basket so that the next shot is in one of the two zones where you will most likely sink the putt.
Last bit of advice, do the same stuff all the time. If you like to hold the disc out in front of you then bounce a little, set up, visualize and then throw...do that every time. Remember to always keep up that routine that works for you. Even do this in the gimmee zone... nothing worse then missing an easy putt b/c you thought it would just go in and you boff it.